The present invention relates to the technical field of the extraction of metals, more particularly of iron, and/or of non-noble nonferrous metals and/or noble metals from ores and/or ore residues, preferably from pyrite residues or pyrite cinder, more particularly roasted pyrites.
The present invention relates more particularly to a method for obtaining/recovering metallic iron or iron compounds, more particularly iron chloride, from ores and/or ore residues, preferably from pyrite residues, more preferably from roasted pyrites obtained in the production of sulfuric acid.
Furthermore, the present invention relates to a corresponding recovery plant, more particularly for obtaining/recovering metallic iron or iron compounds, more particularly iron chloride, from ores and/or ore residues, preferably from pyrite residues, very preferably from roasted pyrites obtained in the production of sulfuric acid, it being possible for the plant of the invention to be used to implement the method of the invention.
The present invention accordingly also relates to the use of the recovery plant of the invention in the method according to the invention for obtaining/recovering metallic iron or iron compounds, more particularly iron chloride, from ores and/or ore residues.
In general, ores comprise, in particular, chemical compounds of metals, such as iron compounds, in the form of iron oxides, iron carbonates and iron sulfides, for example, it being possible for the metal compounds in question to be present in the ore as a mixture with nonferrous minerals.
The most important iron ores include magnetite, limonite, hematite and siderite. While iron in the case of magnetite is in the form of iron (II, III) oxide (Fe3O4), iron in hematite is encountered fundamentally as iron (II) oxide (Fe2O3). In siderite, furthermore, iron is primarily in the form of iron (II) carbonate (FeCO3).
Known additionally, however, are natural ores in which iron is present primarily in conjunction with sulfur. These include, in particular, pyrite, which on account of its metallic luster and its brassy yellow coloring is also known synonymously as fool's gold.
In particular, pyrite includes a series of further technologically and/or economically significant metal components, such as zinc, copper, cobalt and lead, for example, and also further ingredients based on calcium and silicon, which in general, as a result of the primary industrial utilization of pyrite for the purpose of producing sulfuric acid, are not valorized and hence remain, so to speak, unutilized in the material or resulting roasted pyrites.
As mentioned above, iron in pyrite is present in particular in the form of the sulfide, more particularly as iron (II) disulfide or FeS2, in this context, pyrite represents the most widespread sulfide mineral. On an industrial scale, it is used as starting material for producing or obtaining sulfuric acid, with the resulting residues being referred to as pyrite cinder or, synonymously, as purple ore or roasted pyrites.
In the course of the production of sulfuric acid using pyrite as starting material, the general procedure in the prior art is to subject pyrite, as sulfidic metal ore, to roasting in the presence of atmospheric oxygen, with iron sulfide present in pyrite giving rise first of all to sulfur dioxide (SO2) and to iron oxides in different oxidation states. Subsequently, particularly as part of what is called a contact method or in a contact kiln, the resulting sulfur dioxide is oxidized using a catalyst, vanadium pentoxide, for example, and in the presence of additional oxygen, to form sulfur trioxide (SO3). Subsequent adsorption and/or reaction with water then produces sulfuric acid (H2SO4).
In summary, therefore, the production of sulfuric acid starting from pyrite is carried out in particular in the form of a four-stage operation, the method comprising the following steps:                (i) roasting of pyrite, for example in a fluidized bed roasting furnace, for obtaining sulfur dioxide starting from iron sulfide or iron disulfide or iron (II) disulfide (with the corresponding chemical reaction equation 4FeS2+11O2→2Fe2O3+8SO2);        (ii) subsequent gas purification, particularly for purifying sulfur dioxide obtained beforehand;        (iii) oxidation of sulfur dioxide to sulfur trioxide (with the corresponding chemical reaction equation 2SO2+O2→2SO3), a reaction which can be carried out with the use of catalyst in a contact reactor or tray reactor; and        (iv) adsorption of sulfur trioxide with hydrous sulfuric acid, more particularly concentrated hydrous sulfuric acid, for the purpose of obtaining further sulfuric acid, with the sulfur trioxide acting as an anhydride of the resulting sulfuric acid (with the chemical reaction equation SO3+H2SO4(H2O)→2H2SO4).        
Generally speaking, on the industrial scale, sulfuric acid is employed in very large quantities and in numerous sectors of the chemical industry: a large proportion of the sulfuric acid produced goes into the production of fertilizers. Furthermore, sulfuric acid acts as a starting product or intermediate in the production of other industrially relevant products, such as catalysts, surfactants, acids, such as hydrofluoric acid, sulfates, drying agents, reaction auxiliaries, and the like. Not least on account of the numerous possible uses of sulfuric acid, it is clear that there is a high demand for it: accordingly, worldwide production of sulfuric acid has exceeded the order of magnitude of 200 million metric tonnes per annum, making sulfuric acid globally the most produced chemical.
Against this background as well it is clear that in the production of sulfuric acid using pyrite as starting material, large quantities of pyrite cinder or roasted pyrites result. These, generally speaking, are the waste or residue arising in the form of pyrite from the roasting of the starting materials and starting ores employed. Roasted pyrites, in particular, comprise a solid residue arising in the production of sulfur dioxide or sulfuric acid by thermal treatment of pyrite. The general assumption is that on a worldwide basis, at least 20 million metric tonnes of roasted pyrites are obtained annually in connection with the production of sulfuric acid.
The roasted pyrites are generally stored or land filled at the site of production, there already being very large stocks of roasted pyrites present on a worldwide basis in connection with the production of sulfuric acid, which has been practiced from the end of the 19th Century onward. Since the pyrite forming the basis for the production of sulfuric acid, before being processed, is generally comminuted or ground, the resulting roasted pyrites take the form, generally, of a finely particulate and, in particular, relatively homogeneous substance.
As far as the resulting pyrite cinder or roasted pyrites, generally, are concerned, they comprise large amounts of iron and also economically relevant amounts of further metals, including noble metals as well, which are not removed from the starting material in the course of sulfuric acid production, meaning that roasted pyrites as such, against this background, are a valuable raw material for the recovery of economically relevant quantities of metals, including noble metals.
In particular, roasted pyrites comprise iron oxides in the form of FeO, Fe2O3 (hematite) and/or Fe3O4 (magnetite), and residual amounts of FeS2 (iron disulfide), which are responsible in particular for the reddish coloration of roasted pyrites. As well as silicon dioxide (SiO2) and sulfates, particularly in the form of calcium sulfate (CaSO4), roasted pyrites also include significant quantities of the metals zinc, copper, cobalt, titanium, manganese, vanadium, chromium and lead. Furthermore, roasted pyrites also comprise noble metals, more particularly in the form of gold and/or silver. In this regard as well, roasted pyrites harbor a not least economically high potential in relation to the extraction or recovery of metals, non-noble nonferrous metals, and noble metals.
In this respect it is also notable that iron, with a weight fraction of 95% in relation to the total metals utilized, is the most widely used metal globally. Iron, for example, constitutes the principal constituent of steel. The reason for the extensive use of iron lies not only in its wide availability but also, in particular, in the fact that iron has outstanding properties in respect of strength and toughness, especially insofar as iron is present in the form of alloys with other metals, such as chromium, molybdenum, and nickel. On account of these properties, iron is a basic material for many sectors of industry. In particular, iron in the form of steel is used in producing vehicles, ships, and across the construction sector, as steel-reinforced concrete, for example. A further factor is that iron represents a ferromagnetic metal and, consequently, is also important for large-scale industrial use in the area of electromagnetism, such as in generators, transformers, electrical inductors, relays, and electrical motors. In this context, iron is used either in pure form or in combination, for example, with silicon, aluminum, cobalt or nickel as a soft-magnetic core material for the guiding of magnetic fields and/or for the shielding of magnetic fields, or for increasing the inductivity. Iron is also used in the chemical sector, especially in the form of iron powder. In 2010, worldwide production of crude iron exceeded the figure of 1000 million metric tonnes. This shows that on a worldwide basis there is a very high demand for iron.
Against this background, initial approaches in the prior art have been pursued into making economic use of the roasted pyrites resulting as a waste product of sulfuric acid production.
Thus, for example, the residue in the form of pyrite cinder or roasted pyrites that remains in the getting of sulfuric acid is used in blast furnaces. The focus in this regard is on the obtention of iron, with the underlying methods occasionally not being economically and environmentally optimal, however, and recovery of further substances not being provided.
Furthermore, U.S. Pat. No. 4,259,106 A relates to a method for the roasting of an iron-containing starting material, such as roasted pyrites, which also comprises further metals, the intention being to subject the further metals to a chlorination. With regard to the chlorinating reagent, calcium chloride is the authoritative reference point. In this context, chlorination only of non-iron metals is envisaged, the intention being that iron as such should remain in the melt. A disadvantage, moreover, is the high energy consumption associated with the underlying method.
Moreover, GB 1 236 345 A is not aimed at recovery of iron specifically. In particular, the intention is only that there should be chlorination of non-iron metals at the same time as the roasting of the starting material. On the basis of the chlorinating agents used and the process regime selected, moreover, there is a high resulting corrosion activity, which is detrimental particularly to the apparatus on which the method is based.
Furthermore, EP 0 538 168 A1 is not directed to the chlorination and recovery of iron from roasted pyrites. Instead, this document is aimed at optimizing the cyanide leaching indicated for the recovery of gold and silver, there being no intention to recover metallic iron. The process regime selected, moreover, is economically disadvantageous.
Furthermore, CN 101 067 163 A describes a treatment method for pyrite where neither roasting nor chlorination is envisaged. For this reason as well, the isolation of individual components from the raw material is not very efficient.
Furthermore, CN 102 605 172 A relates to a method involving pyrite roasting, which envisages subsequent reduction of the cinder using a biomass. As a result of the carbon present in the biomass, the aim is to reduce iron(III) oxide to metallic iron. The resulting metallic iron is to be isolated via magnetic separation. Extensive recovery of further metals is not envisaged.
Moreover, CN 102 502 527 A is geared to the use of iron sulfate as a starting substance, which with pyrite and elemental sulfur is to be reacted to give iron powder. Chlorination within the recovery process is not envisaged. Selective separation of different metal components is not effectively ensured.
CN 102 251 067 A is aimed at a treatment of pyrite or pyrite cinder without chlorination, the intention being to remove metallic constituents by means of leaching methods. Disadvantages here, however, are the high level of chemical usage and also the occasionally low selectivity of the separation procedure.
CN 102 225 374 A relates to magnetic separation of iron following removal of other metals from pyrite cinder. Chlorination of metallic components is not envisaged. Nor is targeted and selected separation of different metal components envisaged.
Furthermore, CN 102 121 059 A relates to a roasting method for pyrite. Chlorination of metallic components is not described. Furthermore, iron is reduced using carbon. A disadvantage in this case, however, is that occasionally the resulting metallic iron is not of high purity, since impurities may result from the carbon used for the reduction.
CN 102 344 124 A describes the conversion of iron sulfate via the monohydrate form into sulfuric acid, iron and iron oxide, with pyrite being used as starting material. There is no description of specific chlorination. Similarly, extensive separation and recovery of different metals is not envisaged.
Moreover, GB 1 350 392 A relates to the obtention of non-noble nonferrous metals from pyrite after roasting and chlorination of the non-noble nonferrous metals. Chlorination of iron is not envisaged. The iron component is to remain in the form of iron oxide in the residue. Accordingly, efficient separation of all the components is not possible.
U.S. Pat. No. 4,576,812 A relates to a method whereby iron chloride is used as a chloride source: starting from iron chloride and employing oxygen, the aim subsequently is to produce iron (III) oxide, which is then used for the recovery of iron. Roasting of the starting material is not described, and so occasionally dispersant starting materials are present.
Furthermore, DE 2 005 951 A is directed to a method for processing pyrite cinder to form feedstocks for blast furnaces. The pyrite cinder in this case is to be pelletized and burnt in a rotary furnace in the presence of calcium chloride, the purpose of the calcium chloride being to oxidize the iron. No further processing or separation is envisaged, and/or is impossible on account of the specific process regime.
DE 637 443 A relates to the reduction of iron chloride using steam and optionally coal, starting from materials containing ferrous sulfide, the aim being to obtain elemental sulfur.
The scientific publication Trumbull R. C. et al., “Transactions of the Institution of Mining and Metallurgy”, 58, 1949, pages 1 to 31, relates to a method for the treatment of pyrite cinder according to the so-called Henderson process. In accordance with this method, the pyrite cinder is first of all comminuted and then subjected to roasting in the presence of sodium chloride. From the residue obtained in this way, non-noble nonferrous metals are removed. There is, however, no intention of recovering iron from the pyrite cinder treated in this way. The roasting takes place in the presence of sodium chloride at temperatures of above 350° C. and in the presence of oxygen.
The scientific publication Pitsch H. et al., Revista de Metalurgia, 6, 1970, pages 490 to 500, relates to a method for removing non-noble nonferrous metals from pyrite cinder using chlorinating reagents in the form of chlorine gas or calcium chloride. There is no intention to recover iron from the treated pyrite cinder. The pyrite cinder is chlorinated in an oxidizing atmosphere at high temperatures at 1000 to 1200° C., with the consequence that any resultant iron(III) chloride is immediately converted to iron (III) oxide and, consequently, there is no iron(III) chloride present after the chlorination.
The processing methods known in the prior art for metallic ores, especially pyrite, or for waste products arising in the processing of these ores, such as roasted pyrites, are therefore often associated with the drawback that on the one hand the underlying methods are technically complex and are carried out using a high volume of chemicals, and secondly that comprehensive separation and/or recovery of different metal components is not possible. Equally, some of the plant used for the methods in question, owing to the complex process regime, is costly and inconvenient.